The rotor circuit of synchronous machines excited without brushes by means of rotating rectifiers is inaccessible. To be able to monitor the rotor circuit for possible ground leaks nevertheless, auxiliary brushes have been provided in the past which were applied temporarily during the tests. However, such auxiliary brushes must be serviced and are also trouble-prone.
Accordingly, it is an object of the invention to provide an arrangement for monitoring the rotor circuit of a brushlessly excited synchronous machine and for detecting possible ground leaks without the need to utilize brushes.